Conventionally, paper, plastic film, metal plate, cloth, or any of other web materials is supplied in large rolls wound on cylindrical cores. When the rolls are being wound or unwound, the cores are usually mounted on rotatable shafts. Inflated air shafts are typically used to lock the core to the rotatable shaft so that the rolls may rotate with the rotatable shaft as a unit.
Typically, an air shaft may be implemented as a button model, a serrated key model, a lug or strip model, or a plate model based on its appearance. Each of the above types of air shaft is adapted to insert into the cores of rolls of a specific material. However, these types of air shaft have some disadvantages. Thus, a manufacturer of the art devises a plate model air shaft as disclosed in Taiwanese Utility Model Patent No. 475,593 (“593” Patent). The “593” Patent is proposed as an improvement of the typical button model air shaft which has gripping members on its outer surface adapted to urge against an inner surface of the cores of rolls of material when the air shaft is inflated. However, there is an imbalance of force between portions of the cores of rolls of material being urged and portions of the cores of rolls of material being not urged. As a result, the cores of rolls of material tend to permanently deform or even twist. This is not desirable.
The “593” Patent as an improvement of the typical button model air shaft is a plate model air shaft as shown in FIGS. 1 and 2. The air shaft comprises a hollow cylinder 11, a plurality of curved inner plates 12 arranged as a hollow cylindrical member inside the hollow cylinder 11 and spaced therewith, a plurality of curved outer plates 13 arranged as a hollow cylindrical member on an outer surface of the hollow cylinder 11, an airtight bladder 14 in the shape of a hollow cylinder provided on an inner surface of the inner plates 12, a plurality of radial cylindrical sliding members 15 interconnecting the inner and the outer plates 12 and 13 through the hollow cylinder 11, and a resilient member (not shown) provided between the inner plates 12 and the hollow cylinder 11. The inflated bladder 14 expands to push the inner plates 12 outwardly toward the outer plates 13 which in turn tightly engage with (i.e., lock) an inner surface of the core of a roll 16. As such, the roll 16 rotates with the plate model air shaft as a unit in a material winding or unwinding operation. As stated above, the outer plates 13 are curved and are formed of an elastomeric material. Thus, the outer plates 13 may elastically deformed in response to inward pressure exerted thereon by the roll 16. As such, the outer plates 13 are completely engaged with the inner surface of the roll 16. As an end, the roll 16 is fully supported and its circumference can be maintained.
However, the above types of air shaft have disadvantages. In detail, material is wound on the roll 16 in use. The roll 16 is discarded after unwinding the material from the roll 16. This is a waste in view of environmental protection. Also, manufacturers of the roll 16 do not have the desire to recycle rolls 16 since it can incur a great cost. Further, the plate model air shaft cannot directly wind a web material thereon due to the following reasons.
Firstly, the plate model air shaft can maintain its circumference in use. However, there is a gap “s” between any two adjacent outer plates 13 of the plate model air shaft. Thus, portions of a web material may be pinched by the gaps “s” when it is wound on an outer surface of the outer plates 13.
Secondly, the gaps “s” may decrease after deflating the bladder 14. As such, portions of a web material may be pinched by the gaps “s”. As a result, it is impossible of unwinding the material from the plate model air shaft.
Thus, it is desirable to provide a novel air shaft capable of not pinching the cores of rolls 16 of a web material neither in a process of winding same thereon nor in a process of unwinding same therefrom, being environmental friendliness, and without requiring a manufacturer of the roll 16 to recycle same after use.